Linnaeus's Two-Toed Sloth

Linnaeus's Two-Toed Sloth

Unau, Southern two-toed sloth, Linne's two-toed sloth

Choloepus didactylus
Population size
Life Span
20-40 yrs
0.27 km/h
4-8.5 kg
46-86 cm

Linnaeus’s two-toed sloth, or otherwise known as Unau, is thought to be the slowest mammal in the world. The coloration of this animal's fur varies from gray-brown to beige with characteristic greenish cast as a result of algae, growing in the fur. The outer layer of its fur is long and bristly, while the under layer is made up of shorter, finer hairs. Unlike in other mammals, Unau's coat grows from its stomach to the back. On its hind legs, Linnaeus’s sloth exhibits 3 toes, whereas forelegs of the animal have only 2 webbed toes. Unau is a very light-weight animal as compared to other mammals of its size. This helps the animal collect leaves from long, thin branches.


The range of Linnaeus’s sloth stretches through the Central America and northern South America and some parts of Brazil and Peru. The preferred habitat of this species is high canopy of the tropical rain forest. Home range of each individual is usually about 10 acres.

Linnaeus's Two-Toed Sloth habitat map

Climate zones

Habits and Lifestyle

Linnaeus’s sloths are usually solitary animals, although females can sometimes be feeding in the same tree. These animals spend as much as 15 - 20 hours per day sleeping. They wake up at night to feed, moving to a new tree each night, but rarely passing more than 40 meters. Most of the time is spent hanging upside down in trees. They use their long claws to cling onto branches of trees. Young often inherit home ranges of their parents. When on land, Linnaeus’s sloths are very clumsy. However, when in the water, they prove to be accomplished swimmers, using their long arms to move through water. Unaus are generally silent animals. However, when threatened, they are known to emit hissing sounds, low cries and moans. Their main tool of self-defense is camouflage, although claws and teeth also allow these animals to defend themselves.

Diet and Nutrition

Linnaeus’s sloths are primarily herbivores. Their diet mainly consists of berries, leaves, small twigs, fruits and other vegetation, complemented with small prey such as insects. The typical matter of feeding is harvesting leaves with their lips.

Mating Habits

Year-round, peak season occures in March-April
6 months
1 baby
1 year
baby, pup

Little is known about the mating system of Linnaeus’s sloths. However, it is suggested that they may exhibit either polygynous or polygynandrous (promiscuous) mating systems, and females appear to initiate mating. Linnaeus’s sloths mate year-round. According to observations, these animals may have a peak season, occurring in March-April. Females of this species produce young once a year. Gestation period lasts for 6 months, yielding a single baby, which lives clinging into the belly of its mother for the first 5 weeks of its life. Independence is reached at 1 year old, although the young sloth often continues to associate with its mother until 2 years old. Age of sexual maturity is 3 years old for females and 4 - 5 years old for males.


Population threats

The biggest threat to the overall population of this species is habitat destruction as a result of hunting for their coat, meat and claws as well as logging of their rainforest range. As extremely slow animals, Linnaeus’s sloths are often hit by cars on roads, passing through forests, which they inhabit.

Population number

According to IUCN, the Linnaeus’s two-toed sloth is widely distributed but no overall population estimate is available. Currently, this species is classified as Least Concern (LC) on the IUCN Red List.

Fun Facts for Kids

  • The scientific name of Linnaeus’s sloth is ‘Choloepus’, meaning "lame foot" in Greek and referring to the extreme slowness of this animal. As a matter of fact, Linnaeus’s sloth is the slowest animal in the world. Algae, growing on their fur, is highly beneficial, serving as a camouflage and helping them hide from predators.
  • The structure of their fur enhances algae growth. In addition, these animals are likely to get nutrients either by licking algae or absorption through their skin.
  • The stomach of this animal consists of 4 parts. Digestion process is very slow and may take as long as 1 month to digest a meal of tough leaves. Hence, the sloth gets very little energy, which is only enough for slowly moving around.
  • When on the ground, they usually move at a speed of 2 meters (6.5 feet) per minute. When in trees, these animals are a little bit faster, moving at a speed of 3 meters (10 feet) per minute.
  • These arboreal animals leave the trees only once a week, descending on the ground to defecate.
  • Sloths are accomplished swimmers, using breaststroke technique, like humans. In order to swim, they drop themselves off of tree branches into the river.
  • These sloths rarely drink water, getting all required moisture from juicy plants they consume.


1. Linnaeus's Two-Toed Sloth Wikipedia article -
2. Linnaeus's Two-Toed Sloth on The IUCN Red List site -

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